1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus having the same, and particularly relates to a broadcasting television camera, a cinema camera, a video camera, a digital still camera, a silver halide film camera and the like.
2. Description of the Related Art
An image pickup apparatus such as a broadcasting television camera, a cinema camera, a silver halide film camera, a digital camera and a video camera has been conventionally desired to be provided with a zoom lens which has a reduced size and weight, a high zoom ratio, and besides, an adequate optical performance. Particularly, an imaging device such as CCD and CMOS which are used in a television/cinema camera of a moving image photographing system for professionals has an almost uniform resolving power over the whole imaging range. Because of this, the zoom lens to be used in this system is required to have an almost uniform resolving power from the center to the periphery of the screen. In addition, reduction in size and weight is also required for an imaging form in which mobility and operability are regarded as important.
Particularly, as a zoom lens which is also excellent in photographing for a wide angle of field, there is a positive-lead type four-unit zoom lens which arranges a first lens unit that has positive refractive power and is used for focusing, in the side closest to the object side, and includes four lens units as a whole.
Japanese Patent Application Laid-Open No. H06-242378 discloses a zoom lens which has a first lens unit including three units having negative refractive power, positive refractive power and positive refractive power, respectively, and includes four units as a whole having positive refractive power, negative refractive power, negative refractive power and positive refractive power, respectively, or having positive refractive power, negative refractive power, positive refractive power and positive refractive power, respectively, from the side closest to the object side. Japanese Patent Application Laid-Open No. S63-008619 discloses a zoom lens which has a first lens unit including three units having negative refractive power, positive refractive power and positive refractive power, respectively, and four units as a whole having positive refractive power, negative refractive power, positive refractive power and positive refractive power, respectively, sequentially from the object side.
However, in a conventional technology disclosed in Japanese Patent Application Laid-Open No. H06-242378, it is difficult to further widen the angle of the zoom lens and further reduce the size and weight thereof at the same time. A zoom lens which has lens units having negative refractive power arranged in a side closer to the object side than a stop, as in Embodiment 1 or 2 in Japanese Patent Application Laid-Open No. H06-242378, is disadvantageous to the widening of the angle of the zoom lens and reduction in the size and weight thereof, because it is difficult to suppress the diameter of a lens unit existing in an image side of the second lens unit and the first lens unit. Embodiment 3 in Japanese Patent Application Laid-Open No. H06-242378 discloses a technology in which a third lens unit has positive refractive power. However, in the Embodiment 3, the third lens unit has a strong refractive power, and accordingly the number of constituting lenses increases. Embodiment 3 also results in having no other choice but to increase the number of lenses constituting the fourth lens unit in order to secure a sufficient F-number and an exit pupil for a strong convergence light emitted from the third lens unit, and as a result, the zoom lens is disadvantageous to the reduction in the size and weight.
On the other hand, the configuration of the first lens unit of the above described zoom lens disclosed in Japanese Patent Application Laid-Open No. S63-008619 cannot appropriately control a principal point of the first lens unit, when the angle is further widened, and it is difficult to avoid upsizing of a lens diameter. In addition, in the configuration of focus units as in Japanese Patent Application Laid-Open No. S63-8619, it is difficult to adequately correct the variation of aberration and the variation in the angle of field occurring when an object distance has varied.